In recent years, studies are performed for interconnecting wireless systems using different techniques to provide an environment for performing communications in various places without being fixed to a wireless system. As an example of the communication environment that is not fixed to a wireless system, there is a mobile communication system in which a W-CDMA (Wideband Code Division Multiple Access) system and a wireless LAN (Local Area Network) system are interconnected.
Here, the W-CDMA system and the wireless LAN system are compared in terms of communication area. As to the W-CDMA system, since a cell radius of a base station is so wide to be several kilometers and communication is continued even though moving over base stations, a service area can be largely widened.
On the other hand, as to the wireless LAN system complying with the IEEE802.11 standard, a communication range of an access point is so narrow to be several tens to several hundreds meters, and handover between access points is not defined. Handover is operation for automatically switching connecting access points when a terminal performs communication while moving. Therefore, as to the wireless LAN system, the terminal cannot move between the access points while performing communication so that the service area cannot be largely widened.
Next, the W-CDMA system and the wireless LAN system are compared in terms of transmission speed. As to a wireless LAN system complying with the IEEE802.11a and g standards, the maximum transmission speed is 54 Mbps which is higher than the transmission speed 14.4 Mbps of the W-CDMA system.
Therefore, in a mobile communication system in which the W-CDMA system and the wireless LAN system are interconnected, optimal communication can be performed taking advantage of the merit of the wireless system in which different techniques are used, in which the W-CDMA system is used while moving at high speed and the wireless LAN system is used when performing high speed communication in a static state, for example.
In addition, in a mobile communication system, packet communication is performed for example. In the packet communication, a scheduler is used for multiplexing many packets into limited wireless resources. In the packet communication, in order to support services, which should satisfy strict delay requirement, such as a voice service and a real time communication service and the like, priorities are provided for each service or each terminal to perform scheduling according to the priorities.
In the non-patent document 1, procedures and a system are disclosed for performing handover and the like between a wireless LAN system and a UMTS (Universal Mobile Telecommunications System). In the non-patent document 2, a terminal is disclosed for performing handover between different types of wireless access networks (RAN). The patent document 1 discloses a wireless communication system that changes priorities of packets of a newcomer terminal that performs handover into a new service area and an old terminal of the service area according to a predetermined definition.    [Patent document 1] Japanese Laid-Open Patent Application No. 2003-110574.    [Non patent document 1] UMA-Unlicensed Mobile Access (UMA) technology (http://www.umatechnology.org/) UMA User Perspective (Stage 1) R1.0.0    [Patent document 2] IEICE General Conference, B-5-133, RAN overlay type MIRAI system, 2003